Weight detecting apparatuses, which detect weights of objects by weight detectors such load cells, have been widely used in various fields. Patent reference 1 (Japanese Laid-Open Patent Publication No. H8-110261) and patent reference 2 (Japanese Laid-Open Patent Publication No. H8-136330) have disclosed examples of weight detecting apparatuses, which are configured to eliminate disturbance due to vibrations for further improving detection precision.
Referring to FIG. 5, the weight detecting apparatus disclosed in the patent reference 1 includes a weight detecting load cell (load cell for measurement) A1 and a vibration detecting load cell (load cell for dummy) A2, which are fixed at their fixed ends to a fixed base (floor) B. An object table C placing an object X is coupled to a free end of weight detecting load cell A1. A balance weight (i.e., a metal weight of a known weight) D is attached to a free end of vibration detecting load cell A2.
Thereby, when the fixed base B vibrates as indicated by an arrow due to vibrations of the floor, the weight detecting load cell A1 issues a detection signal produced by superimposing floor vibration components on the weight of the object X, on the other hand, the vibration detecting load cell A2 issues a detection signal according to floor vibration components. For example, as shown in FIG. 6, the weight and vibration detecting load cells A1 and A2 have cell sensitivity characteristics usually varying according to magnitudes and others of target loads. For allowing arithmetic processing between the detection signals provided by these load cells A1 and A2, arithmetic processing for correction is effected on the detection signals. More specifically, processing is performed to subtract the detection signal from the vibration detecting load cell A2, which is arithmetically processed for correction in a predetermined manner, from the detection signal of the weight detecting load cell A1. In other words, vibration components on a device installation side are removed from the detection signal of the weight detecting load cell A1 so that only the signal matching with the weight of the object X can be obtained.
As shown in FIG. 7, the weight detecting apparatus disclosed in the patent reference 2 has a weight detecting load cell (first load cell) A1 having a fixed end, which is fixed to the fixed base B on the floor. A transporting conveyor (transporting means) C1 is fixed to a free end of the weight detecting load cell A1 via a vibration detecting load cell (second load cell) A3. In this structure, the transporting conveyor C1 is coupled to a free end of the vibration detecting load cell A3.
For example, when the transporting conveyor C1 with the object X placed thereon changes its position as represented by an arrow (i.e., when a certain kind of vibrations occur) due to driving of a motor (not shown in Figures), which is a drive source of the transporting conveyor C1, the weight detecting load cell A1 issues the detection signal, in which a motor vibration component is superimposed on the weight of the object X, and the vibration detecting load cell A3 issues the detection signal corresponding to the motor vibration component. Similarly to the weight detecting apparatus disclosed in the patent reference 1, arithmetic processing for correction is effected on the detection signals for allowing arithmetic processing between the detection signals provided by the weight and vibration detecting load cells A1 and A3, which have different characteristics. More specifically, processing is performed to subtract the detection signal of the vibration detecting load cell A3, which is arithmetically processed for correction in a predetermined manner, from the detection signal of the weight detecting load cell A1. In this manner, vibration components on an object placing side are removed from the detection signal of the weight detecting load cell A1 so that only the signal matching with the weight of the object X can be obtained.
The weight detecting apparatuses in the patent references 1 and 2 suffer from the following problems.
In the weight detecting apparatus disclosed in the patent reference 1, if the object table C is formed of the transporting conveyor C1 as disclosed, e.g., in the patent reference 2, vibration components that originate from the transporting conveyor C1 are superimposed on the detection signal of the weight detecting load cell A1. However, the device does not have a component or structure for removing the vibration components occurring on the object placing side. This lowers the detection precision.
In the weight detecting apparatus disclosed in the patent reference 2, vibration components of the vibration of the fixed base B are superimposed on the detection signals of the weight and vibration detecting load cells A1 and A3. However, the device does not have a component or structure for removing the vibration components occurring on the device installation side. This likewise lowers the detection precision.